The present disclosure relates to a display device having a self-luminous light-emission element including an organic layer and a method of producing the display device.
In recent years, as a display device substituting for a liquid crystal display, an organic EL (electroluminescence) display using a self-luminous organic light-emission element including an organic layer has been made practical. The organic EL display is of self-luminous type and thus has a wide viewing angle compared to a liquid crystal and the like, as well as having sufficient responsiveness to a high-definition high-speed image signal.
For the organic light-emission element, so far, an attempt has been made to improve display performance by introducing a resonator structure, and controlling light produced in a luminous layer, like improving a color purity of a luminous color or increasing luminous efficiency (for example, see International Publication No. WO01/39554). For instance, in a top-emission system in which light is extracted from a surface (top surface) opposite to a substrate, there is adopted a structure in which an anode electrode, an organic layer, and a cathode electrode are laminated sequentially via a drive transistor on a substrate; and multi-path reflection of light from the organic layer is caused between the anode electrode and the cathode electrode.
In an ordinary organic EL display, for example, an organic light-emission element that emits red light, an organic light-emission element that emits green light, and an organic light-emission element that emits blue light are arranged sequentially and repeatedly in an image display region. Those luminous colors vary depending on a material forming an organic layer of each color. Therefore, it is desirable to form the organic layers individually for the respective luminous colors, when forming each organic light-emission element. It is to be noted that in an ordinary organic EL display, an anode electrode and an organic layer are divided for every organic light-emission element, whereas a cathode electrode is one-piece to be shared by two or more (preferably, all) organic light-emission elements. Here, the organic layers in the respective organic light-emission elements adjacent to each other are separated from each other by an insulating layer. This insulating layer has an opening to define an emission region in each organic light-emission element.
Formation of the organic layer is performed, for example, by vapor deposition. At the time, the deposition is performed using a shadow mask having an opening according to an emission region and thus, it is desirable to align the opening of the insulating layer defining the emission region precisely with the opening of the shadow mask. Recently however, there has been a trend to narrow the width of the insulating layer and reduce the interval between the adjacent organic light-emission elements, in order to improve the ratio of the emission region of all the organic light-emission elements to the entire image display region, namely, a numerical aperture. For this reason, it is expected in future that if the above-mentioned interval is further reduced, it will be difficult to fill each emission region with a predetermined organic layer sufficiently with reliability. This is because there is such a concern that it might be difficult to ensure sufficient accuracy of alignment between the opening of the insulating layer and the opening of the shadow mask, or sufficiently ensure processing accuracy of the shadow mask itself, or the like. When the opening of the insulating layer is not filled with the organic layer sufficiently with reliability due to such a production error, desired luminance at a predetermined position in the image display region is not obtained, and it is difficult to perform correct image display corresponding to an inputted image signal.
To address such a disadvantage, for example, it is conceivable to employ a method of making the opening of the shadow mask larger than the opening of the insulating layer, and forming an organic layer greatly extending off the emission region to the insulating layer. This makes it possible to fill each emission region with a predetermined organic layer reliably.
In this case however, ends of the organic layers of organic light-emission elements adjacent to each other are in a condition of overlapping each other. Therefore, there is a possibility that a hole injection layer in one organic layer overlaying the end of the other organic layer may touch a cathode electrode covering those organic layers. In such a case, a conduction path is formed between an anode electrode and the cathode electrode via the hole injection layer, and a leakage current flows. Therefore, there is a possibility that control of driving each organic light-emission element may not be performed sufficiently, and normal image display in an organic EL display may be disturbed. In particular, when a leakage current flows between organic light-emission elements that emit light of different colors, this may cause a color mixture in the display image.
Therefore, the present applicant has already proposed a method of providing a separation film having a wall surface shaped like an overhang to surround each light-emission element, and separating organic layers as well as cathode electrodes in the adjacent light-emission elements from each other (for example, see Japanese Unexamined Patent Application Publication No. 2010-44894).